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Method and apparatus for detecting and compensating for white shading errors in a digitized video signal

  • US 5,157,497 A
  • Filed: 02/25/1991
  • Issued: 10/20/1992
  • Est. Priority Date: 02/25/1991
  • Status: Expired due to Term
First Claim
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1. A white shading correction apparatus for detecting and compensating for white shading errors in a digitized video signal representing a sequence of horizontally scanned video images of a flat white calibration target including a plurality of horizontal lines, each horizontal line comprising a plurality of pixels, comprising:

  • inspection means for inspecting said plurality of pixels;

    calculating means for calculating a white level correction coefficient for each pixel inspected by said inspecting means, said calculating means including a first accumulator means for summing pixel amplitudes in each said horizontal line of said horizontally scanned video image, having a first output, said first output being the summed value of said pixel amplitudes for each said horizontal line, a second accumulator means for inspecting a plurality of horizontal lines and compiling from said horizontal lines a plurality of vertical column data derived from said plurality of pixels comprised within said horizontal lines, having a second output, said second output being the summed value of said compiled vertical column data for each column found in said plurality of pixels comprised within said horizontal lines, and processing means for computing said correction coefficients from said summed values output from said first output and second output derived from said first and second accumulator means respectively; and

    correction mean for correcting video images subsequent to said video image representing a flat white calibration target, said correction based upon said white level correction coefficients calculated in said calculating means, thereby compensating said subsequent video images present in said digitized video signal for white shading errors.

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